Google upset the online display ad market yesterday, after it confirmed the takeover of Invite Media.

Immediately following the buyout, claims of “conflict of interest” were thrown at the world’s largest ad broker.

Invite Media currently allows advertisers to buy display ad spots from a wide cross section of ad exchanges, including Google’s own DoubleClick Ad Exchange, Yahoo!’s Right Media and Microsoft’s AdECN.

Mountain View’s rivals in the online display ad biz are worried that swallowing Invite Media means the company now controls too much of the market.

One such company, The Media Innovation Group (MIG), owned by WPP, one of the world’s largest ad agencies, expressed concerns about the acquisition in confidential papers seen by The Register.

The firm said that Google’s takeover of Invite Media, which the search giant reportedly spent $70m on, could stifle the display ad business. It acknowledged that Yahoo!’s Right Media was already seeing its share of the market fall, and suggested that Carol Bartz’s company could consider an acquisition of its own to compete with Google’s increasing dominance.

MIG has its own digital advertising product - dubbed B3 - which it describes as the “leading agency tool for acquiring and optimising display advertising”.

The main concern among MIG and other online ad platform makers is that Google’s decision to buy the New York and Philadelphia-based Invite Media real-time bidding ad exchange could cause “conflict of interest” problems among other key web players such as Microsoft and Yahoo!

Google, for its part, said it was simply responding to its desires to invest “significantly in the display advertising ecosystem” with this buy.

The company said it planned to improve Invite Media’s technology and products as a separate platform. Eventually Google hopes to make it “work seamlessly” with its DoubleClick for Advertisers (DFA) product.

“Invite Media’s platform will of course continue to be available to any agency or advertiser, whether they use DFA or not,” said Google product management veep Neal Mohan, who was clearly keen to settle jingly nerves among its competitors.

He added that the DoubleClick Ad Exchange would “continue to provide exactly the same open and neutral access to ad space for multiple buyers, partner support and API availability as it has always done”.

It’s unclear at this stage whether the acquisition will be scrutinised by regulators in the US and Europe, however. ®